Flexible board and electronic device

Abstract

A flexible board includes a flexible body including a first principal surface and a second principal surface, and a linear conductor provided in the body and closer to the first principal surface than to the second principal surface. The body is bent inwardly with respect to the first principal surface along an inward bending line crossing the linear conductor and also outwardly with respect to the first principal surface along an outward bending line crossing the linear conductor. The inward bend of the body has a larger mean curvature radius than the outward bend of the body.

What is claimed is: 
     
       1. A flexible board comprising:
 a flexible body including a first principal surface and a second principal surface; and a linear conductor provided in the body and located closer to the first principal surface than to the second principal surface; wherein the body is bent inwardly with respect to the first principal surface to include an inward bend along an inward bending line crossing the linear conductor and also outwardly with respect to the first principal surface to include an outward bend along an outward bending line crossing the linear conductor; 
 the inward bend of the body has a larger mean curvature radius than the outward bend of the body; and 
 a first portion of the body adjacent to the outward bend is parallel or substantially parallel to a second portion of the body adjacent to the inward bend, the first portion and the second portion are at opposite sides of the inward bend and the outward bend. 
 
     
     
       2. The flexible board according to  claim 1 , further comprising:
 a first ground conductor provided at a side of the first principal surface with respect to the linear conductor; and 
 a second ground conductor provided at a side of the second principal surface with respect to the linear conductor; wherein 
 the first ground conductor is less distant from the linear conductor than the second ground conductor is. 
 
     
     
       3. The flexible board according to  claim 2 , wherein the first ground conductor is smaller in area opposed to the linear conductor than the second ground conductor is. 
     
     
       4. The flexible board according to  claim 1 , wherein the body is made of a thermoplastic resin. 
     
     
       5. The flexible board according to  claim 1 , wherein
 the body includes a protective layer defining and functioning as the second principal surface; and 
 the protective layer has a higher relative permittivity than a remainder of the body. 
 
     
     
       6. The flexible board according to  claim 1 , wherein the flexible board defines a high-frequency signal line. 
     
     
       7. The flexible board according to  claim 1 , wherein the body includes a plurality of dielectric sheets. 
     
     
       8. The flexible board according to  claim 7 , wherein at least two of the plurality of dielectric sheets have different thicknesses. 
     
     
       9. The flexible board according to  claim 1 , wherein the linear conductor is a signal line defined by a patterned metal foil. 
     
     
       10. The flexible board according to  claim 1 , wherein one surface of the linear conductor has a roughness that is different from another surface of the linear conductor. 
     
     
       11. The flexible board according to  claim 2 , wherein one of the first and second ground conductors includes openings and the other of the first and second ground conductors does not include openings. 
     
     
       12. The electronic device according to  claim 1 , further comprising first and second ground conductors that define a tri-plate stripline structure with the linear conductor. 
     
     
       13. An electronic device comprising: a housing; and a flexible board accommodated in the housing; wherein the flexible board includes; a flexible body including a first principal surface and a second principal surface; and a linear conductor provided in the body and located closer to the first principal surface than to the second principal surface; the body is bent inwardly with respect to the first principal surface to include an inward bend along an inward bending line crossing the linear conductor and also outwardly with respect to the first principal surface to include an outward bend along an outward bending line crossing the linear conductor;
 the inward bend of the body has a larger mean curvature radius than the outward bend of the body; and 
 a first portion of the body adjacent to the outward bend is parallel or substantially parallel to a second portion of the body adjacent to the inward bend, the first portion and the second portion are at opposite sides of the inward bend and the outward bend. 
 
     
     
       14. The electronic device according to  claim 13 , further comprising a metallic body in contact with the second principal surface in the outward bend of the body. 
     
     
       15. The electronic device according to  claim 13 , wherein the electronic device is a cell phone. 
     
     
       16. The electronic device according to  claim 13 , wherein the flexible board defines a high-frequency signal line. 
     
     
       17. The electronic device according to  claim 13 , wherein the body includes a plurality of dielectric sheets. 
     
     
       18. The electronic device according to  claim 17 , wherein at least two of the plurality of dielectric sheets have different thicknesses. 
     
     
       19. The electronic device according to  claim 13 , wherein the linear conductor is a signal line defined by a patterned metal foil.